The present invention relates to engine control systems, and more particularly to the control of spark retard in displacement on demand engine control systems.
Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder can be operated using four cylinders. Cylinder deactivation improves fuel economy by reducing pumping losses.
To smoothly transition between activated and deactivated modes, the internal combustion engine must produce torque with a minimum of disturbances. Otherwise, the transition will not be transparent to the driver. In other words, excess torque will cause engine surge and insufficient torque will cause engine sag, which degrades the driving experience.
For example for an eight-cylinder engine, intake manifold pressure is significantly lower during eight-cylinder operation than during four-cylinder operation. During the transition from eight to four cylinders, there is a noticeable torque reduction or sagging in four-cylinder operation until the intake manifold reaches a proper manifold pressure level. Increasing the manifold pressure before the transition causes a torque surge until the transition is complete. Spark retard can be used smooth the transition.
An engine control system and method calculates spark retard during cylinder deactivation for a displacement on demand engine. A torque reduction calculator calculates a torque reduction signal based on desired and measured air per cylinder. A spark retard (RTD) calculator generates a RTD signal based on the torque reduction signal.
In other features, the RTD signal is a negative offset from a minimum spark advance for best torque (MBT). A final RTD calculator generates a final RTD signal based on the RTD signal, an MBT signal and a spark advance (SA) signal.
In still other features, a cylinder deactivation enable circuit generates a cylinder deactivation enable signal A selector selectes one of a desired deactivated air per cylinder and an activated air per cylinder based on the cylinder deactivation enable signal.
An engine control system and method calculates spark retard during cylinder activation for a displacement on demand engine. A torque reduction calculator calculates a torque reduction signal based on desired and measured air per cylinder. A spark retard (RTD) calculator generates a RTD signal based on the torque reduction signal.
In other features, an activation gain circuit provides a gain signal. A multiplier generates a product by multiplying the gain signal by the torque reduction signal, wherein the product is input to the RTD calculator.
In yet other features, the RTD signal is a negative offset from a minimum best torque (MBT). A final RTD calculator that generates a final RTD signal based on the RTD signal, an MBT signal and a spark advance (SA) signal.
In still other features, a cylinder reactivation circuit generates a cylinder reactivation enable signal. A multiplier generates a second product of the cylinder reactivation enable signal and the final RTD signal.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.